1. Field of the Invention
The present invention relates to a liquid crystal display device and a method of fabricating the same, and more particularly, to a liquid crystal display device and a method of fabricating the same capable of reducing the number of mask processes in fabricating the liquid crystal display device.
2. Discussion of the Background Art
A liquid crystal display device (hereinafter, referred to as LCD device) is light weight, slim, and low in power consumption, and thus is used for terminals of various information devices or video systems instead of a cathode ray tube (CRT). In particular, a TFT-LCD device including a thin film transistor has an excellent response characteristic and is suitable for a large number of pixels, and thus can implement a display device with high image quality and a wide screen.
In such a flat panel display, an active device such as a thin film transistor (TFT) is included in each pixel to drive a display device. This type of driving method of the display device is often called an active matrix driving method.
In the active matrix system, the active device is disposed in each of pixels arranged in a matrix to drive the pixel.
The general active matrix LCD device will now be described briefly.
N M pixels are arranged vertically and horizontally in a general LCD device. Each pixel of a thin film transistor LCD device includes a thin film transistor formed at a crossing region of a gate line and a data line that receive a scan signal and an image signal respectively from an external drive circuit.
The thin film transistor includes a gate electrode extending from the gate line a source electrode extending from a data line, and a drain electrode connected to a pixel electrode and a semiconductor layer formed between the source electrode and the drain electrode.
When a voltage is applied to the gate electrode through the gate line, the thin film transistor applies a data voltage applied to the source electrode through the data line to the drain electrode through a semiconductor channel layer.
When the data voltage is applied to the drain electrode, the data voltage is applied to the pixel electrode connected to a drain electrode, generating a voltage difference between the pixel electrode and a common electrode of the pixel. Then, a molecular arrangement of liquid crystals between the pixel electrode and the common electrode changes due to the voltage difference, thereby changing its optical transmittance.
That is, a visual difference results between the pixel to which the data voltage is applied and the pixel to which the data voltage is not applied.
Therefore, the LCD device serves as a display device through an assembly of pixels having visual differences.
A TFT-LCD device that employs a twisted nematic (TN) mode has a drawback of a limited viewing angle. However, an in plane switching (IPS) LCD device has recently been proposed to improve somewhat the limited viewing angle.
However, even though the IPS-LCD device implements a wide viewing angle, it still has problems of the low aperture ratio and transmittance. In order to solve such problems, a fringe field switching (hereinafter, referred to as FFS) LCD device is proposed.
A method of fabricating the FFS LCD device will now be described with reference to FIGS. 1A to 1E.
FIGS. 1A to 1E are cross-sectional views illustrating a method of fabricating a liquid crystal display device according to the related art.
Referring to FIG. 1A, indium tin oxide (ITO) that is a transparent material is deposited on a substrate 11, and then the ITO is selectively etched through exposure and development by a first mask process using a photolithography process to form a common electrode 13.
Referring to FIG. 1B, a metal material is stacked on the substrate 11, and then the metal material is etched through exposure and development by a second mask process using a photolithography process to form a gate electrode 15a. At this point, a storage node electrode 15b, a gate pad part 15c, and a data pad part 15d are also formed by etching the metal material.
Referring to FIG. 1C, a gate insulating layer 17, an active layer and a metal conductive layer are sequentially stacked on the overall substrate 11, and then the metal conductive layer and the active layer are sequentially etched through exposure and development by a third mask process using a diffraction exposure mask to form an active layer pattern 19, a source electrode 21a, and a drain electrode 21b at the same time.
Referring to FIG. 1D, a passivation layer 23 is formed on the overall substrate 11, and then the passivation layer 23 is selectively etched by a fourth mask process to form a contact hole 25a exposing the drain electrode 21b. At this point, in etching the passivation layer 23, openings 25b and 25c exposing the gate pad part 15c and the data pad part 15d are formed as well as the contact hole 25a. 
Referring to FIG. 1E, a transparent conductive material such as ITO is deposited on the overall substrate 11 including the contact hole 25a, and then the transparent conductive layer is selectively etched through exposure and development by a fifth mask process to form a pixel electrode 27a electrically connected to the drain electrode 21b. At this point, in etching the transparent conductive layer, a gate pad 27b and a data pad 27c connected to the gate pad part 15c and the data pad part 15d respectively through the openings 25b and 25c are formed as well as the pixel electrode 27a. 
However, as described above, the method of fabricating the LCD device according to the related art has the following drawbacks.
The method of fabricating the LCD device according to the related art requires at least five mask processes, that is the first mask process of forming the common electrode, the second mask process of forming the gate electrode, the third mask process of forming the active layer and the source/drain electrodes, the fourth mask process of forming the contact hole for connection with the drain electrode, and the fifth mask process of forming the pixel electrode.
Therefore, because at least five mask processes are required in fabricating the device, the fabricating process is complicated, and consequently the fabrication cost is increased.